The 1980 Symposium will be on Photobiology and Photomedicine. Theoretical and practical aspects of solar and artificial sources of electromagnetic radiation will be discussed. Such physical factors as heat, hydration and wind in photomediated skin injury, will also be included. The photochemistry of melanin and responses of the melanocyte to ultraviolet radiation will be presented. In addition to natural means of protection, methods of assessing the effectiveness of chemical sun protective agents will be addressed. The role of electromagnetic radiation in production of skin carcinogenesis in man and in experimental animal models will be reviewed. Mechanisms of photoinjury come about from such abberrant metabolism as the porphyrias, disturbed DNA repair processes as xeroderma pigmentosum, or photochemical alteration of man-made chemicals which cause photoallergy. The differential susceptibility of T and B lymphoid cells may allow the selective depletion of these cells as they course through the skin leading to alterations in the immune state. Therapeutic uses of EMR include UV-A with the photosensitizing psoralen compounds now widely used in the treatment of psoriasis. Also, the treatment of neonatal hyperbilirubinemia with light is now understood at the molecular level, and this is a real therapeutic advance.